Method for contention free traffic detection

ABSTRACT

The invention discloses a method for detecting priority of data frames comprising the steps of extracting (S 1 ) a bit pattern from a predetermined position in a frame, comparing (S 2,  S 3 ) said extracted bit pattern with a search pattern, and identifying (S 4 ) said received frame as a priority frame in case said extracted bit pattern (BP) matches with said first search pattern (SP). By this method, the priority of a data frame can easily be detected. The invention also proposes a corresponding device for detecting priority of data frames.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of International ApplicationPCT/EP99/10097 having an international filing date of Dec. 17, 1999 andfrom which priority is claimed under all applicable sections of Title 35of the United States Code including, but not limited to, Sections 120,363 and 365(c).

FIELD OF THE INVENTION

[0002] The present invention relates to a method and a device fordetecting priority of data frames in a network.

BACKGROUND OF THE INVENTION

[0003] This invention relates in general to the field oftelecommunications, more precisely to Wireless Local Area Networks(WLAN) and Electrical and Electronics Engineers (IEEE) 802.11 WLANstandard.

[0004] The IEEE 802.11 Wireless Local Area Network specificationspecifies a so-called Contention Free Period (CFP), which is a period oftransmission time that is free from the normal contention based airtimereservation. The length and duration of CFP are configurable parametersin Access Point (AP), so that the start of CFP is repeated after one ormore Delivery Traffic Indication Message (DTIM) intervals (see IEEE802.11 standard). The CFP and its relationship to the so-called ContentPeriod (CP) is schematically illustrated in FIG. 12. As can be seen, aCFP repetition interval contains a Content Free Period (CFP) and aContent Period (CP). Each CFP begins with a beacon frame that contains aDTIM element.

[0005] The purpose of this CFP is that it can be used for deliveringhigh priority traffic, which has higher real time requirements thannormal traffic. The CFP is controlled by the so-called PointCoordination Function (PCF) in an Access Point (AP). The standardspecifies the PCF operation in basic level, but does not specify how thePCF should be controlled or how some traffic should be identified ashigh priority traffic. These things are considered to be out of thescope of the standard.

[0006] Information within data frames is marked as having a highpriority by using certain fields in some protocol frames or headers.However, the Access Point (AP) usually processes only frames on theMedium Access Control (MAC) layer such that the AP can not easily accessinformation regarding the priority of certain data blocks within theframes, since this information is processed in higher layers.

[0007] Thus, for getting priority information, conventionally the frameswhich are to be transmitted through an Access Point (AP) had to besearched for these fields which indicate the priority state of theactual data frame. This means that in all frames all fields had to bechecked, all the headers had to be analyzed, starting from the outermost headers, until the right field in the header had been found.

[0008] Since all frame headers are parsed when detecting priority, thismeasure has a high reliability.

[0009] However, this measure is very complex, takes a long time andrequires a large amount of processing. Furthermore, the traffictransferred in WLAN can be practically anything, including complextunneling protocols.

[0010] Therefore, all the frame headers and protocols which can beincluded in the data frames transmitted via the network have to beknown. Hence, the amount of information needed for identifying the datais huge. This huge amount of information is typically too heavy tohandle in quite small and low price equipment like WLAN access points(AP).

[0011] In addition, it has to be considered that every time newprotocols are introduced, the access point has to be updated, at leastby software updates. This is also required in case protocols alreadyused are changed.

[0012] Thus, conventionally such a transmission differentiation based onpriority was not conducted at all. That is, the existing systemsaccording to the IEEE 802.11 standard do not separate traffic based onpriority. In these conventional systems, the Content Free Period (CFP)is only used to deliver traffic from the Access Point (AP) to stations,treating all frames equally.

SUMMARY OF THE INVENTION

[0013] Therefore, the object underlying the invention resides inremoving the above drawbacks of the prior art and to provide a method bywhich priority traffic can easily be distinguished from normal trafficwithout the need of a complex processing.

[0014] This object is solved by a method for detecting priority of dataframes in a network comprising the steps of extracting a bit patternfrom a predetermined position in a frame, comparing the extracted bitpattern with a search pattern, and identifying the received frame as apriority frame in case the extracted bit pattern matches with the firstsearch pattern.

[0015] Alternatively, the above object is solved by a device fordetecting priority of data frames in a network comprising a receivingmeans for receiving data frames, an extracting means for extracting abit pattern from a predetermined position of a data frame, a comparingmeans for comparing the extracted bit pattern with a predeterminedsearch pattern, and an identifying means for identifying the receivedframe as a priority frame in case the extracted bit pattern matches withthe first search pattern.

[0016] Thus, a priority which is defined in a higher-level layer caneasily be detected by comparing a corresponding bit pattern with asearch pattern without further processing of the received frame. By themethod and the device according to the invention, simply a bit patternis extracted at a position in the frame, where the priority informationis known to be located. This bit pattern is compared with a searchpattern which corresponds to that bit pattern, which would be located atthe above position in case that a priority is set for the actual frame.Thus, it is not necessary to process and analyze the received frame,i.e., to process higher-level layers in order to obtain priorityinformation.

[0017] Hence, when adopting the IEEE 802.11 WLAN standard, the prioritycan be detected in the Medium Access Control (MAC) layer which is alow-level layer. That is, the method can easily find higher prioritytraffic from the stream of MAC layer frames. Therefore, the method doesnot need any knowledge of the upper layer protocols.

[0018] Consequently, according to the method of the invention, certaintraffic can be defined to have higher priority than other traffic whenit is handled in an IEEE 802.11 WLAN Access Point (AP). The method isdesigned so that it is as lightweight as possible to execute in a lowcost and possibly low performance AP.

[0019] Furthermore, the method is protocol-independent and so flexiblethat all the configuration may be done in external configuration programand the Access Point does not need to know anything about the processedtraffic.

[0020] Further advantageous developments are set out below.

[0021] In particular, the predetermined position in the frame is definedby the offset of the bit pattern in the frame. Thus, the position of thebit pattern to be extracted and examined can accurately be defined.

[0022] Furthermore, the offset and the search pattern are included in aninformation element. This information element can be produced by anexternal program such that the device according to the invention and thedevice performing the method according to the invention does not have togenerate the search pattern and the offset. Thus, the structure of thedevice does not have to be complex.

[0023] In addition, in case new protocols or modified protocols areintroduced in the network, it is not necessary to reconfigure thenetwork element (i.e., the device) performing the method. It is onlynecessary to provide new information elements including the new offsetand the new search pattern, which can be effected by an externalconfiguration program. For this, it is not necessary to install newsoftware in the network element or to install new hardware. It is noteven necessary to shut down the network element for a new configuration.Hence, the method is very flexible.

[0024] Moreover, the bit pattern can be masked by using a mask. Then,the masked bit pattern is compared with the search pattern instead ofcomparing the bit pattern with the search pattern. By this measure,single bits can easily be extracted from the bit pattern. This isadvantageous in case the bit pattern is extracted in form of bytes. Forexample, a bit pattern can include two bytes, whereas for the prioritydetection only two bits of each byte are required. These two bits caneasily be extracted by using the mask.

[0025] The mask can also be included in the information elementdescribed above.

[0026] If necessary, also a plurality of different bit patterns, searchpatterns, offsets and—optionally—masks can be used to detect priority ofthe frames. By this measure, priority information can be detected whichis located at different positions within a data frame.

[0027] Alternatively, a plurality of different priority levels can beprovided for the frames. For detecting different priority levels, aplurality of different bit patterns, search patterns, offsetsand—optionally—masks can be used to detect the plurality of differentpriority levels. By this measure, also different priority levels caneasily be detected.

[0028] Hence, a plurality of different information elements can be used.For example, one certain priority can require a plurality of informationelements, while another certain priority can require only one particularinformation element.

[0029] A received frame can be forwarded to a priority queue in case theframe is detected to be a priority frame during a special period forsending priority traffic. The priority queue serves to transmit the datapriority frames in the network faster than normal frames. This measureis especially advantageous in an IEEE 802.11 WLAN since in thisstandard, a Contention Free Period is defined, as described above.

[0030] In addition, the duration of the special period for sendingpriority traffic can be adjusted according statistical informationregarding the priority frames sent. Thus, the special period, i.e., theContention Free Period, can be adjusted corresponding to the load ofpriority traffic on the network.

[0031] Furthermore, for obtaining the statistical information, the totalnumber of priority frames and the number of priority frames outside thespecial period can be counted. Then, it can be decided on the basis ofthe count values obtained whether the special period has to be increasedor decreased.

[0032] In addition, in the IEEE 802.11, a data+CF-poll frame is defined.Preferably, this data+CF-poll frame can be used for transmittingpriority frames in case of a symmetrical high priority traffic betweenthe Access Point and stations in the network.

[0033] Furthermore, the invention proposes a method for generatingpriority detecting information necessary for the above method anddevice. This method comprises the steps of analyzing a data frame,identifying a bit pattern indicating a priority state, defining theidentified bit pattern as a search pattern, and locating the bit patternwithin the data frame. By this method, the necessary priority detectioninformation can easily be provided. For example, this method can beemployed by a configuration program that is externally run, for example,in one of the wireless stations which are connected by air with theAccess Point.

[0034] The above method for generating priority detecting informationmay further comprise the steps of determining the offset of thelocation, and producing an information element including the offset andthe search pattern. Optionally, also the mask for masking the bitpattern mentioned above can be determined and included in theinformation element.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be more readily understood withreference to the accompanying drawings in which:

[0036]FIG. 1 shows a main system overview;

[0037]FIG. 2 shows a process for checking priority of frames accordingto a first embodiment;

[0038]FIG. 3 shows an example for a frame to be examined by the processaccording to the first embodiment;

[0039]FIG. 4 shows a frame priority detecting device according to thefirst embodiment;

[0040]FIG. 5 shows an example of pattern matching with two differentinformation elements according to a second embodiment;

[0041]FIG. 6 illustrates a flow chart of a frame sending procedureduring Content Free Period (CFP) according to the second embodiment;

[0042]FIG. 7 shows relevant parts of a Point Coordinator (PC) accordingto a third embodiment;

[0043]FIG. 8 illustrates a flow chart of a frame sending procedureduring Content Free Period (CFP) according to the third embodiment;

[0044]FIG. 9 illustrates a flow chart of a frame sending procedureduring contention period according to the third embodiment; and

[0045]FIG. 10 illustrates a flow chart of a procedure for CFP parametertuning according to the third embodiment;

[0046]FIG. 11 shows a flow chart of a method for obtaining prioritydetection information; and

[0047]FIG. 12 illustrates the relationship between Content Free Periods(CFP) and Content Periods (CP) according to IEEE 802.11.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0048] In the following, preferred embodiments of the invention aredescribed in more detail with reference to the accompanying drawings.

[0049]FIG. 1 shows an overview of the main system used in theembodiments. The system is a normal IEEE 802.11 Basic Service Set (BSS)containing one Access point (AP) 2 and one or more wireless stations(STA) 3 to 5. The AP may or may not be connected to another wired orwireless network 1. The purpose of the AP 2 is to transmit the trafficbetween the wireless stations or between wireless stations and thenetwork 1 which is connected to the AP 2.

[0050] All the network components function according to the IEEE 802.11standard. This presented set-up is a typical representation of thecoverage area of one AP. The whole wireless network usually consists ofseveral of these kinds of subsystems. An external configuration programmay run in one of the stations in the wireless network or it may residein some other host and be connected to AP with a wire. In this example,the configuration program is executed in the wireless station 3.

[0051] In the following, a first embodiment which shows the basic ideaof the invention is described with respect to the flow chart shown inFIG. 2 and an example for a Medium Access Control (MAC) layer frameshown in FIG. 3.

[0052] The procedure shown in FIG. 2 is executed by the Access Point AP2 every time a Medium Access Control (MAC) layer frame has beenreceived.

[0053] In step S1, the AP 2 extracts a bit pattern from a given positionin the received frame. The bit pattern can be a pattern of two bytes,for example. However, the length of the bit pattern can be selectedarbitrarily. The extracted bit pattern is indicated by BP in FIG. 2. Instep S2, the extracted bit pattern BP is compared with a predeterminedsearch pattern SP. If in step S3 it is decided that both patterns match,it is determined in step S4 that the actual frame is a priority frame.On the other hand, if it is decided in step S3 that both patterns do notmatch, it is determined in step S5 that the actual frame is not apriority frame. After identifying the priority of the frame, the framecan be treated according to the identified priority.

[0054] Thus, the frame can easily be examined whether it is a priorityframe or not without the need for analyzing the data format in the MAClayer frame itself, i.e., without knowing protocols of the higherlayers.

[0055] The position of the bit pattern to be extracted is defined by theoffset OS from the start of the MAC frame, as shown in FIG. 3. Thus, theAP 2 requires only information regarding the offset OS and the searchpattern SP for checking priority of certain MAC frames.

[0056] This information can be provided by an external configurationprogram. The configuration program can be executed in one of thewireless stations, for example. Alternatively, it can be executed in anysuitable network element, including the Access Point itself. For thisconfiguration program it is necessary that the bit positions of thepriority information which are usually set in higher layers are known.Thus, by providing the AP with the offset, the AP does not have toprocess the frame in order to identify priority information. It is onlynecessary to obtain the corresponding bit pattern.

[0057] In the first embodiment, the configuration program is executed inthe wireless station STA 3. The configuration program producesinformation elements which contain the above-described informationregarding the offset OS and the search pattern SP necessary to identifythe priority state of certain MAC frames. These information elements aretransmitted to the AP 2.

[0058]FIG. 4 shows the relevant parts of the Access Point 2 in moredetail. Reference numeral 22 denotes a frame receiver by which framesare received from the wired or wireless network 1 and also from thewireless stations 2 to 5. Reference numeral 23 denotes a bit patternextractor by which the bit pattern BP described above is extracted froma predetermined position. The position is defined by the offset OS, asmentioned above, and the offset is stored in an offset memory 27 whichis accessed by the bit pattern extractor 23. The extracted bit patternBP is forwarded to a comparator 24 which compares the extracted bitpattern BP with the search pattern SP. The search pattern SP is storedin a search pattern memory 25 which is accessed by the comparator 24.The comparison result is supplied to a priority identifying means 26which identifies the actual frame F as a priority frame in case thecomparison results indicates that the bit pattern BP matches the searchpattern SP. Thus, the Access Point (AP) 2 can detect priority frames andcan treat them correspondingly.

[0059] As mentioned above, the external configuration program providesinformation elements which each comprise an offset OS and a searchpattern SP. These information elements are received by an informationelement receiver 28. The receiver 28 analyzes the information elementand supplies the detected offset OS to the offset memory 27 and thedetected search pattern SP to the search pattern memory 25.

[0060] The first embodiment described above illustrates the basicoperation according to the invention. The second embodiment described inthe following describes a further, more detailed example for the highpriority traffic detection method in which the Content Free Period (CFP)defined in IEEE 802.11 standard is used for transmitting detected highpriority frames.

[0061] According to IEEE 802.11, the Content Free Period (CFP) is aperiod which is reserved for transmitting high priority traffic, asdescribed above in the introductory part with respect to FIG. 12. TheCFP is controlled by a Point Coordinator (PC) 21 which is arranged inthe Access Point (AP) 2 shown in FIG. 1. If the high priority traffic istransferred only from the AP 1 to the wireless stations (i.e., in atypical client-server application case), the CFP may be used only fordelivering data from the AP to wireless stations. But, if the nature ofthe high priority traffic is interactive (like a videoconference, forexample), the PC 21 must also poll wireless stations to permit them totransmit also during the CFP. See IEEE 802.11 standard for more detaileddescription about this basic functionality of IEEE 802.11 standard.

[0062] The AP 2 receives MAC layer frames either from the wirelessstation or from the connected wired network. If the destination of theframe is in the wireless network, the AP will check whether the frame ishigh or normal priority traffic. The priority detection requires thatthe AP 2 is configured with the external configuration program to detectthe priority and the required configuration information elements areconfigured to the AP by the external configuration program. The AP alsoneeds to reformat the MAC level header of the frame or encapsulate theframe inside a separate IEEE 802.11 MAC header which is defined in IEEE802.11. The point when the priority detection check is performed (beforeor after IEEE 802.11 MAC header formatting) can be left implementationspecific.

[0063] If the BSS is in a so-called Contention Free (CF) state (i.e.,currently there is a Contention Free Period (CFP)) and the frame is apriority frame, the frame is put in a priority transmit queue, otherwisethe frame is treated like the normal traffic. During the CFP, all theframes in the priority queue are transmitted before any frames from thenormal queue. When the CFP ends, remaining frames in the priority queueare moved to the normal queue and priority queue is flushed.

[0064] According to this embodiment, the priority of a MAC layer frameis detected by using one or more information elements which aretransmitted to the Access Point (AP) 1. That is, one or more bitpatterns with corresponding different offsets are checked whether theymatch with one or more different search patterns. Furthermore, the bitpatterns extracted from the MAC layer frame are also masked by using amask. The mask is also contained in an information element. Thus, theinformation element according to the second embodiment comprises theoffset and the search pattern as according to the first embodiment, andin addition a mask. The mask serves to obtain only particular bits inthe extracted bit pattern and is optional.

[0065] The operation according to the second embodiment is described byreferring to FIGS. 5 and 6. It is noted that for simplifying theillustration, the second embodiment is described with reference to thecase that the priority is detected by using two information elements.

[0066] In FIG. 5 it is shown that two bit patterns BP1 and BP2 areextracted from the MAC layer frame F. The first bit pattern BP1 isextracted with an offset OS1. As illustrated, the first bit patternmatches with the first search pattern SP1. For the first bit patternBP1, no mask has been specified (i.e., no masking is performed).

[0067] However, for the second bit pattern BP1 a mask M2 is specified.In this example, the mask is M2=00010000 such that only the fourth bitis passed through. The resultant bit pattern BP2′ is then compared withthe second search pattern SP2. Here, the second search pattern SP2 andthe masked bit pattern BP2′ match. Since also the first search patternSP1 matches with the first bit pattern BP1, it is decided that theactual frame F is a high priority frame.

[0068] According to the second embodiment, the frame F which has beendetected as a priority frame, is transmitted in the Contention FreePeriod (CFP). That is, it is put on a high priority queue. This processis described in the following by referring to the flow chart shown inFIG. 6.

[0069] The process shown in this flow chart is performed during theContent Free Period, i.e., in case the CFP is active. In step S61, theAccess Point (AP) 2 waits for receiving a frame which is to betransmitted further to the wireless stations 3 to 5 (FIG. 1). In stepS62, the bit patterns BP1 and BP2 are extracted from the frame F, asshown in FIG. 5. In step S63, the bit pattern BP2 is masked with themask M2 to obtain a bit pattern BP2′, as described above. Since no maskhas been specified for the first bit pattern BP1, no corresponding stepfor the first bit pattern BP1 is performed.

[0070] Then, in step S64, it is checked whether both bit patterns BP1and BP2′ match with the search patterns SP1 and SP2, respectively. IfSP1 and BP1, and SP2 and BP2′ respectively match, it is decided that thereceived frame F is a high priority frame, and the frame F is put in thepriority queue (step S65). This is effected by the Point Coordinator(PC) 21 arranged in the Access Point (AP) 2. If the patterns do notmatch (NO in step S64), the received frame F is put in the normal queue,as shown in step S66.

[0071] As described above, the Point Coordinator (PC) 21 puts a priorityframe in the priority queue in case the Contention Free Period (CFP) isactive. However, in case the CFP is inactive, the frame goes to thenormal queue so that it does not have to wait for the CFP to start. Whenthe CFP starts, the PC flushes the normal queue and places the unsenthigh priority frames in the priority queue. Thus, when the PointCoordinator (PC) 21 notices that the frame which should be sent is ahigh priority frame, it puts this frame in the normal or high priorityqueue depending on the current state of the network.

[0072] As mentioned above, the use of two information elements is onlyan example. The number of information elements can be more than two. Byusing a plurality of information elements, it is also possible todistinguish between different priority levels. For example, theconfiguration program can give the following data to the Access Point bywhich three priorities (i.e. priority 1, priority 2 and priority 3) canbe distinguished. It is noted that these three priorities can eachrepresent different priority levels (e.g., priority 1 represents thehighest priority while priority 3 has the lowest) or can represent equalpriority levels.

[0073] Priority 1 Information:

[0074] Information element 1: offset 1 and search pattern 1

[0075] Information element 2: offset 2 and search pattern 2

[0076] Information element 3: offset 3 and search pattern 3

[0077] . . .

[0078] Information element n: offset n and search pattern n

[0079] Priority 2 Information:

[0080] Information element 1: offset 1 and search pattern 1

[0081] Priority 3 Information:

[0082] Information element 1: offset 1 and search pattern 1

[0083] Information element 2: offset 2 and search pattern 2

[0084] The AP then checks whether a received frame matches with all theinformation elements of the first group containing the informationelements for priority 1. That is, for each information element it ischecked whether a bit pattern at the offset included in the informationelement matches with the search pattern included in the informationelement. If this is the case for all information elements, then theframe has the priority 1.

[0085] If the frame does not match with all information elements listedin the first group, then the AP tests the same frame with all theinformation elements (one, in this example) of the second groupcontaining the information elements for priority 2. If the bit patternextracted at the off set 3 in the frame matches with the search pattern3 included in information element 3, it is decided that the frame hasthe priority 2.

[0086] However, if the patterns do not match, then the AP checks thepriority 3 information. That is, the frame is checked whether it matcheswith information elements 1 and 2. If this is the case, the frame hasthe priority 3. If the frame still does not match, it has no priority.

[0087] Next, a third embodiment is described, according to which thePoint Coordinator (PC) 21 collects statistics about the high prioritytraffic sent and adjusts the parameters for the CFP.

[0088] In detail, the PC 21 counts the high priority packets during theevery so-called Delivery Traffic Indication Message (DTIM) interval (seeIEEE 802.11 WLAN standard). Furthermore, it also counts how much ofthose packets are transmitted outside the CFP and how much during theDTIM interval containing CFP but outside CFP. The PC saves statistics ofthe previous N DTIM intervals, where N is at least the CFP repeatinginterval. The PC then checks the statistics after every DTIM intervalthat contains CFP and adjusts the CFP length and interval accordingly.The frame handling and statistics collection during the CFP is presentedin FIG. 8 and during the contention period in FIG. 9.

[0089] The PC 21 according to the third embodiment is shown in FIG. 7 ingreater detail. As derivable therefrom, the PC comprises a plurality ofcounters which are used by a PC controller 211 to control the CPF. Apriority frames counter (PFC) 212 serves to count all priority framesreceived. A counter for priority frames outside CFP (PFOCFP) counter 213serves to count all priority frames which are received during thecontent period, i.e., when CFP is inactive. A CFP DTIM counter 214serves to count all priority frames which are received in an DTIMinterval containing a Contention Free Period (CFP). As mentioned above,the PC 21 forwards the received priority frames either to the normalqueue 215 or to the priority queue 216 depending on the current state ofthe network.

[0090] The flowchart shown in FIG. 8 is almost the same as in FIG. 6.The steps S81 to S86 correspond to the steps S61 to S66 of FIG. 5. Thus,an unnecessary repetition is omitted here. However, in addition to theflow chart shown in FIG. 6, a new step S87 is performed in case patternsSP1 and BP1, and SP2 and BP2′ match. In this step S8, the priority framecounter (PFC) 212 is incremented each time it is decided that an actualframe is a high priority frame.

[0091]FIG. 9 shows a flowchart representing a process performed duringthe content period, i.e., when the CFP is inactive. Here, all receivedframes are put in the normal queue. In case of a high priority frame,several values are counted by the counters of the Point Coordinator (PC)21 for providing statistical information.

[0092] In detail, in step S91 it is waited for a frame, similar to stepS81 of FIG. 8. In step S92, the priority is detected in the way asdescribed in the first or second embodiment. If the actual frame is anormal frame with no priority, the flow advances to step S97 in whichthe frame is put to the normal queue 215. If, however, the actual frameis a priority frame, the flow advances to step S93 in which PFOCFPcounter 213 is incremented. Furthermore, in step S94 also the priorityframes counter 212 is incremented.

[0093] In step S95 it is checked whether the actual DTIM intervalcontains a Content Free Period (CFP). If this DTIM interval contains aCFP, the CFP DTIM counter 214 is incremented in step S96 before the flowadvances to step S97. Otherwise, the flow advances directly to step S97.Thereafter, the routine is ended.

[0094] The statistical information regarding the priority frames areused as described in the following with reference to FIG. 10.

[0095] As shown in FIG. 10, the procedure is started in an DTIM intervalafter the end of the Content Free Period (step S101). In step S102, thepercentage of priority frames sent outside of the CFP is checked.Depending on the result, different processes are executed, as describednext.

[0096] If the percentage of high priority traffic sent outside of CFP ishigher than a certain high alarm level HAL, the PC 21 will startcorrective actions. These processes are illustrated on the right side ofthe flow chart shown in FIG. 10.

[0097] The alarm level is 100%—percentage of the high priority trafficthat must be send inside the CFP in any case. For example, if it isknown that the traffic which requires an almost real-time treatmentrequires a priority traffic of 30%, the alarm level is set to 70%. Thealarm level can be fixed or it can be dynamically adjustable.

[0098] When the alarm level HAL is reached, the PC will next check thepercentage of high priority traffic sent during the DTIM intervals notcontaining the CFP. This is effected in step S107 in which thedifference between the count values of the PFOCFP counter 213 and theCFP DTIM counter 214 is calculated, wherein the difference is brought inrelation to the value of the priority frames counter (PFC) 212. If it ismore than the alarm level HAL, the PC will make the CFP interval to behalf of the original (if it is not already one DTIM interval), asdescribed in step S108.

[0099] Next, in step S109, the PC 21 will check if the percentage ofhigh priority traffic sent outside of the CFP during the DTIM intervalscontaining CFP is also higher than the alarm level. This percentage P iscalculated as follows:

CFP DTIM counter/(PFC−(PFOCFP−CFP DTIM counter))/100)

[0100] If this percentage is higher than the alarm level, the PC 21 willdouble the duration of the CFP (if not already maximum possible) in stepS1010. The alarm level used in the different steps may be the same ordifferent according to the wanted system behavior.

[0101] If it is decided in step S102 that the percentage of highpriority traffic sent outside the CFP drops below a low alarm level LAL,the PC 21 will start decreasing the CFP in order to give the normaltraffic also a reasonable chance to be delivered in time. The low alarmlevel LAL is the percentage of the high priority traffic that can besend outside the CFP if needed. In order that the system can worksmoothly, the low alarm level should be less than 100%—high alarm levelHAL.

[0102] When the alarm level LAL is reached, the PC 21 will next checkwhat is the percentage of high priority traffic sent during the DTIMintervals not containing the CFP in step S103 which corresponds to stepS107 described above. If it is less than alarm level, the PC will makethe CFP interval to be double of the original in step S104. Next, the PC21 will check if the percentage of high priority traffic sent outside ofthe CFP during the DTIM containing CFP is also lower than the alarmlevel LAL. This is effected in step S105 which corresponds to step S109described above. If this percentage is lower as the alarm level LAL, thePC 21 decreases the duration of the CFP with the amount of the previousaddition in step S106. The alarm level LAL used in the different stepsmay be the same or different according to the wanted system behavior.

[0103] If it is decided in step S102 that the percentage of priorityframes outside the Content Free Period (i.e., the count value of thePFOCFP counter 213 with respect to the count value of the priority framecounter 212) is between the low alarm level LAL and the high alarm levelHAL, the flow advances directly to step S1011 in which all counters 212,213 and 214 are reset. Then, the procedure is ended.

[0104] Next, a fourth embodiment is described. The structure andprocedures according to this embodiment is similar to the embodimentsdescribed above. However, in this embodiment the nature of the highpriority traffic is checked. In particular, it is considered whether thehigh priority traffic is symmetrical, i.e., whether the high prioritytraffic from a wireless station to the Access Point (AP) 2 is the sameor almost the same as the high priority traffic from the AP 2 to thewireless station.

[0105] During the Content Free Period (CFP) the wireless stations(terminals) are not allowed to transmit unless the PC 21 polls them.Therefore, they will register themselves to PC to be placed in a pollinglist. In order to get the best benefit from this traffic control,wireless stations in the WLAN must be able to identify the high prioritytraffic and send that traffic during the CFP.

[0106] In case of the symmetrical high priority traffic between the AP 2and the wireless stations, the configuration information (from theexternal configuration program) contains a field telling that this issymmetrical high priority traffic. When the Point Coordinator (PC) 21 inthe AP 2 detects that the high priority traffic is symmetrical and thereceiving station is pollable during the Content Free Period (i.e., isCF-pollable), it will send it to the terminal inside a so-calleddata+CF-poll frame instead of normal data frame during the CFP. Thedata+CF-poll frame is a special data frame, defined in the IEEE 802.11standard, that allows the receiving station send one data frame duringthe CFP after receiving the data+CF-poll frame. During the contentionperiod, the symmetrical traffic does not cause any special processes.The use of data+CF-poll frame enables equal high priority datadelivering performance to both directions.

[0107] The PC 21 must ensure that other wireless stations in the pollinglist gets polled according to the standard even when deliveringsymmetrical high priority traffic.

[0108] In the following, the configuration program used for generatingpriority detection information used in the above embodiments isdescribed in more detail.

[0109] The method adopted in the configuration program is described byreferring to the flowchart shown in FIG. 11.

[0110] In step S111, a bit pattern (consisting, for example, of one ortwo bytes) which indicates the priority information is identified in thedata frame. The identified bit pattern is defined as the search pattern(SP) in step S112. In step S113, the location, that is, the offset ofthe identified bit pattern (i.e., the search pattern) inside the dataframe is determined. Thereafter, an information element containing thedetermined offset and the identified search pattern is produced in stepS114. Finally, in step S115 the information element is sent to theAccess Point and the routine ends.

[0111] In a similar way, also the optional mask (as used in the secondembodiment) can be obtained. Therefore, an additional step is requiredwhich is performed after the bit pattern identifying step S112 such thatthe mask is defined. It is also possible to produce a plurality ofinformation elements, as used in the second and third embodiment, alsoby taking into account a plurality of different priority levels.

[0112] Next, an example is described in which frames (containing IPpackets) to be sent to a particular IP-adress should have high priority.In this case, the identification of the search patterns and the locationof the search patterns can be performed as follows: The configurationprogram knows that the offset to the destination IP-address from thebeginning of the IP packet (as an example for a data frame) is 32 bytesand the offset from the beginning of the ethernet (version 2) frame tobeginning of the IP packet is 14 bytes. Thus, the actual offset of theIP-address is 46 bytes. The search pattern is the IP-address inquestion. Thus, the necessary information for an information element caneasily be extracted.

[0113] In other cases, it might be necessary that the configurationprogram analyzes frames in order to obtain the relevant information.

[0114] The location for performing the above method within the networkcan be arbitrarily chosen. It may be located in some station in thewireless network, it may be centralized in a place in the wired network,or it may be connected to the AP with a separate cable. In some cases,the configuration program may also be run in the AP, but in this way thebenefit of the configuration program being external will be lost.

[0115] Preferably, the location where the above method, i.e., theexternal configuration program can be performed is in one of thewireless stations 2 to 5. In this way, the program can also “snoop” thetraffic and check whether the traffic is correctly recognized by the AP,that is, whether the high priority traffic is correctly treated. This isbecause in the wireless stations, the data sent with the frames areprocessed and, thus, it is clear whether a received frame is a priorityframe or not.

[0116] When placed in the WLAN, the configuration program can also makecorrections to the AP configurations (i.e., the information elementssent to the AP) based on a traffic monitoring in the WLAN. Theconfiguration program can be run in some notebook PC in WLAN, forexample.

[0117] In rather large networks, however, the best place for theconfiguration program is in the wired network, where all the accesspoints of the network can be controlled with a single configurationprogram.

[0118] The above description and accompanying drawings only illustratethe present invention by way of example. Thus, the embodiments of theinvention may vary within the scope of the attached claims. For example,the embodiments can be arbitrarily combined.

[0119] In particular it has to be noted that the above description ofthe embodiment has been made basically with respect to the IEEE 802.11WLAN standard. However, it has to be noted that this is only an exampleand that it is to be understood that the invention can also be appliedto other suitable network situations.

[0120] Furthermore, in the above embodiments it was basicallydistinguished between priority frames and normal frames, i.e., betweenframes with priority and frames without priority. However, it is alsopossible to distinguish between a plurality of different prioritylevels. For example, the second embodiment can be modified such that thetwo bit patterns are used to distinguish between three differentpriority levels (no priority—medium priority—high priority). Also,different masks for one bit pattern can be used to distinguish betweendifferent priority levels.

1. A method for detecting priority of data frames in a networkcomprising the steps of extracting (S1) a bit pattern from apredetermined position in a frame, comparing (S2, S3) said extracted bitpattern (BP) with a search pattern (SP), and identifying (S4) saidreceived frame as a priority frame in case said extracted bit pattern(BP) matches with said first search pattern (SP).
 2. The methodaccording to claim 1, wherein said predetermined position in said frameis defined by the offset (OS) of said bit pattern in said frame.
 3. Themethod according to claim 2, wherein said offset (OS) and said searchpattern (SP) are included in an information element.
 4. The methodaccording to claim 1, further comprising the step of masking (S63) saidbit pattern (BP2) by using a mask (M2) and comparing the masked bitpattern (BP2′) with said search pattern (SP) instead of comparing saidbit pattern (BP2) with said search pattern (SP).
 5. The method accordingto claim 4, wherein said predetermined position in said frame is definedby the offset (OS2) of said bit pattern (BP2) in said frame, and saidoffset (OS2), said search pattern (SP2) and said mask (M2) are includedin an information element.
 6. The method according to claim 1, wherein aplurality of different bit patterns (BP1, BP2), search patterns (SP1,SP2) and offsets (OS1, OS2) are used to detect priority of said frames.7. The method according to claim 1, wherein a plurality of differentpriority levels are provided and a plurality of different bit patterns(BP1, BP2), search patterns (SP1, SP2) and offsets (OS1, OS2) are usedto detect said plurality of different priority levels.
 8. The methodaccording to claim 1, further comprising the step of forwarding (S65;S85) said received frame to a high priority queue (216) in case saidframe (F) is detected to be a high priority frame during a specialperiod (CFP) for sending priority traffic.
 9. The method according toclaim 8, further comprising the step of adjusting (S101 to S1011) theduration of the special period (CFP) for sending priority trafficaccording statistic information regarding the sent priority frames. 10.The method according to claim 9, further comprising the steps ofcounting (S94) the total number of priority frames; counting (S93) thenumber of priority frames outside said special period (CFP); anddeciding (S103, S107) whether said special period has to be increased ordecreased on the basis of the count values obtained in said countingsteps.
 11. The method according to claim 1, further comprising the stepsof using a data+CF-poll frame defined in IEEE 802.11 for transmittingpriority frames.
 12. A device for detecting priority of data framescomprising a receiving means (22) for receiving data frames (F); anextracting means (23) for extracting a bit pattern (BP; BP1) from apredetermined position of a data frame (F); a comparing means (24) forcomparing said extracted bit pattern (BP; BP1) with a predeterminedsearch pattern (SP; SP1); and an identifying means (26) for identifyingsaid received frame (F) as a priority frame in case said extracted bitpattern (BP) matches with said first search pattern (SP).
 13. The deviceaccording to claim 12, wherein said predetermined position is defined byan offset (OS; OS1, OS2).
 14. The device according to claim 13, whereinsaid offset (OS) and said search pattern (SP) are included in aninformation element.
 15. The device according to claim 12, furthercomprising a masking means for masking said bit pattern (BP2) by using amask (M2), wherein said comparing means (24) compares the masked bitpattern (BP2′) with said search pattern (SP) instead of comparing saidbit pattern (BP2) with said search pattern (SP).
 16. The deviceaccording to claim 15, wherein said predetermined position in said frameis defined by the offset (OS2) of said bit pattern (BP2) in said frame,and said offset (OS2), said search pattern (SP2) and said mask (M2) areincluded in an information element.
 17. The device according to claim12, wherein a plurality of different bit patterns (BP1, BP2), searchpatterns (SP1, SP2) and offsets (OS1, OS2) are used to detect priorityof said frames.
 18. The device according to claim 12, wherein aplurality of different priority levels are provided and a plurality ofdifferent bit patterns (BP1, BP2), search patterns (SP1, SP2) andoffsets (OS1, OS2) are used to detect said plurality of differentpriority levels.
 19. The device according to claim 12, wherein acontrolling means (211) forwards said received frame to a high priorityqueue (216) in case said frame (F) is detected to be a high priorityframe during a special period (CFP) for sending priority traffic. 20.The device according to claim 19, wherein said controlling means (211)adjusts the duration of the special period (CFP) for sending prioritytraffic according statistic information regarding the sent priorityframes.
 21. The device according to claim 20, wherein said controllingmeans (211), in order to obtain said statistic information, accesses toa priority frames counter (212) for counting (S94) the total number ofpriority frames and a counter (213) for counting priority frames outsidesaid special period (CFP), said controlling means (211) deciding whethersaid special period has to be increased or decreased on the basis of thecount values obtained in said counting steps.
 22. The device accordingto claim 12, further comprising a means for transmitting priority framesvia a data+CF-poll frame defined in IEEE 802.11.
 23. Method forgenerating priority detecting information, comprising the steps of:identifying (S111) a bit pattern indicating a priority state, defining(S112) said identified bit pattern as a search pattern, and locating(S113) said bit pattern within said data frame.
 24. The method accordingto claim 23, further comprising the steps of: determining (S113) theoffset of said location, and producing (S114) an information elementincluding said offset and said search pattern.